Method of fabricating a semiconductor device

ABSTRACT

This method provide a method for fabricating a semiconductor device in which waste water generated by a step of processing a semiconductor is filtered to be clean. In the method, removables  12  trapped by a first filter film  10  are used as a second filter film  13 , and clogging of the first filter film  10  is prevented, and an external force such as bubbles is applied to the second filter film  13  to maintain filtering capacity. And when removables are mixed with the filtered water, the filtered water is recirculated again to the tank in which the waste water is stored, and after it is checked that a desired inclusion rate has been reached filtration is started again.

BACKGROUND OF THE INVENTION

1. Field of the invention

This invention relates to a method of fabricating a semiconductordevice, especially a method of processing an waste water generated in astep of forming a semiconductor device and reusing thereof

2. Description of the related Art

Generally, when grinding and polishing or milling of inorganic ororganic solids such as metals and ceramics is carried out, fineparticles are generated. These fine particles are generally washed awayby means of a fluid such as water and discharged as wastewater orsewage. This invention relates to a system for reusing industrialwastewater.

Reducing industrial waste is a serious current ecological theme now andis an important business issue for the 21st century. Among industrialwaste, there are various kinds of wastewater and sewage.

In the following description, water or other fluid substances containingmatters to be removed will be called wastewater. Such wastewater hasremovable matters extracted by an expensive filtration processingapparatus or the like; the wastewater filtered becomes clean and isreused. Wastewater containing unremovable matters is further processedor disposed as industrial waste. Filtered water may be reused orreturned to nature.

However, because of high plant costs related to running a filtrationprocess, employing these apparatuses poses a very difficult problem.

Also, high costs of sewage treatment are a serious problem andtherefore, a system with low initial cost and low running cost isurgently needed.

As an example, wastewater treatment in the semiconductor field will bedescribed below. Generally, when grinding or polishing a metal,semiconductor or ceramic sheet, such factors as limiting temperatureincreases of equipment, improving lubrication, and preventing adhesionof waste produced by grinding and cutting the sheet are considered, anda fluid such as water is supplied to the sheet.

When semiconductor wafers are formed of ingot by grinding and slicingthe ingot into wafers, or when a semiconductor wafer, which is a sheetof a semiconductor material, is diced or back-grinded, pure water issupplied. For preventing a temperature rise of a dicing blade in adicing apparatus and for preventing dicing waste from adhering to thewafer, pure water is made to flow on the semiconductor wafer, or anozzle for discharging water is mounted so that pure water will strikethe blade and the wafer. Also, when the thickness of a wafer is reducedby back-grinding, pure water is supplied for similar reasons.

Wastewater containing semiconductor wafer grinding waste or polishingwaste is filtered and thereby turned into clean water and returned tonature or reused, and concentrated wastewater is collected.

At present, there are two semiconductor manufacturing methods forprocessing wastewater containing mainly Si waste: a coagulatingsedimentation method, and a method combining filtration and acentrifugal separator.

In the coagulating sedimentation method, PAC (poly-aluminum chloride) orAl₂(SO₄)₃ (band sulfate), for example, is mixed with wastewater as acoagulant. Si reactants are produced, and the wastewater is cleaned byremoving those reactants.

In the method of combining filtration and centrifugal separation,wastewater is filtered, and the concentrated wastewater is put in acentrifugal separator and collected as sludge. Water obtained byfiltering the wastewater is discharged into nature or reused.

As shown in FIG. 13, wastewater produced during dicing is collected in araw water tank 201 and fed by a pump 202 to a filtering apparatus 203.Because the filtering apparatus 203 is fitted with ceramic or organicfilters F, filtered water is fed through a pipe 204 to a water tank 205and reused, or it is discharged to the environment.

Since the filters F gets clogged, the filtering apparatus 203 isperiodically washed. This is accomplished by, for example, closing avalve B1 on the raw water tank 201, opening a valve B3 and a valve B2for feeding washing water to the raw water tank 201, and back-washingthe filters F with water from the water tank 205. Wastewater with highlyconcentrated Si waste is returned to the raw water tank 201.Concentrated water in a concentrated water tank 206 is transportedthrough a pump 208 to a centrifugal separator 209, and is separated bythe centrifugal separator 209 into sludge and liquid. The sludgecontaining Si is collected in a sludge collecting tank 210, and theliquid is collected in a liquid tank 211. Also, water of the liquid tank211 in which separated liquid is collected is transported through a pump212 to the raw water tank 201.

Similar methods to those above have also been employed in the collectionof waste produced by grinding and polishing solids and sheets havingmetal materials such as Cu, Fe, Al as their main waste material andsolids and sheets made of inorganic materials such as ceramics.

In the coagulating sedimentation method, a chemical as a coagulant ismixed with the filtered water. However it is very difficult to determinethe necessary and sufficient amount of chemical that the Si waste willcompletely react with, and inevitably excess chemical is introduced andsome chemical will remain unreacted. In contrast, if the amount ofchemical is low, not all the Si waste will coagulate and some Si wastewill remain in the solution.

When the amount of chemical is excessive, some chemical remain in thesupernatant liquid. The supernatant liquid may not be reusable becauseof possible undesirable chemical reactions with the excess chemical. Forexample, filtered water with the excess chemical cannot be reused on awafer during dicing, because it causes an undesirable chemical reaction.

Floc, a reactant of chemical and silicon waste, is produced as asuspended solid. For forming floc, the pH conditions are strict; pH ofabout 6 to 8 must be maintained using an agitator, a pH measuringapparatus, a coagulant pouring device and control devices. For example,for a wastewater processing capacity of 3 m³/hour, a tank with adiameter of 3 meters and a depth of 4 meters (a sedimentation tank ofabout 15 m³) would be necessary, and it becomes a large system requiringan installation area of about 11 meters×11.

Furthermore, some floc may not settle and drift out of the tank, makingthe collection difficult. Hence, there are problems such as a highinitial cost of the filtration system because of the plant size,difficulties of reusing the filtered water, and a high running cost ofthe system because a chemical is used.

The reuse of water is possible with the method combining filtration anda centrifugal separator of 5 m³/hour because filters F (those made frompolysulfone fiber, called UF modules, or ceramic filters) are used inthe filtering apparatus 203. However, four filters F are installed inthe filtering apparatus 203, and because the life of the filters F isabout a year, it is necessary to replace the expensive (approximately500,000 yen/unit) filter at least once a year. Furthermore, the load onthe motor of the pump 202 for applying water to the filtering apparatus203 is large because the filtration method is such that the filters Fare of a pressurized type, and the pump 202 is a high-capacity type. Ofthe wastewater passing through the filters F, about ⅔ is returned to theraw water tank 201. Also, because wastewater containing silicon waste istransported by the pump 202, the internal walls of the pump 202 arescratched, cutting the life of the pump 202 short.

Hence, the cost of electricity for the motor is high and the runningcost is also very high because there are replacement costs of the pump Pand the filters F. FIG. 12 shows comparative data of the above systemand a system of the invention described in the disclosure below. Thereare problems such as the size of the system, replacement of the filters,washing of the filters, and running costs.

To remove solid matter damaging to the earth's environment as much aspossible, various devices must be added, and therefore, the filtrationsystem, must necessarily becomes large, leading to enormous initialcosts and running costs.

SUMMARY OF THE INVENTION

The invention provides a method of manufacturing a semiconductor deviceusing a simple filtering method by which clean water can be obtainedeffectively.

The invention can solve the above-mentioned problems by removingremovables included in a fluid with a filter made from at least some ofthose removables.

When a filter is made with removables, it is possible to form filterpores even smaller than the removables constituting the filter.Therefore it is possible to extract still smaller removables by way ofthese small pores.

The invention can pass a fluid (semiconductor wastewater) includingremovables through a first filter and form on the first filter surface asecond filter consisting of the removables. The second filter canthereby remove other removables from the fluid.

On the first filter surface, a second filter made up of smaller poresthan the pores of the first filter can be made to improve the filteringperformance.

The invention can also recirculate a fluid including removables througha first filter to form on the first filter surface a second filterconsisting of the removables.

As a result of recirculation,a second filter made up of smaller poresthan the pores of the first filter grows on the first filter, andbecause small removables having passed through the first filter are alsorecirculated, the second filter is able to catch even smaller removableshaving passed through the pores of the first filter.

The first filter or the second filter can accommodate removables ofdifferent sizes.

The layered first and second filters with pores can pass fluid throughand are able to catch small removables of different sizes in thewastewater.

The removables can have a particle diameter distribution having twopeaks and the pores of the first filter can have a size between the twopeaks.

With the pores of the first filter being between the two peaks,removables of the larger particle diameter are first trapped. Then astrapped removables are layered on the first filter in variousarrangements, a second filter with smaller pores is formed. The secondfilter is then able to pass fluid and catch smaller removables .

The invention can detect with a detecting means the concentration ofremovables in the fluid passing through the first filter and can stopthe recirculation when the concentration falls below a predeterminedvalue.

A filtered fluid with mixtures of small removables can be recirculatedto create a filter that will catch even those small removables.Therefore, by monitoring the fluid for a predetermined degree ofconcentration of removables as the fluid is recirculated, the fluid canbe filtered to a target filtering accuracy.

The invention can further detect with a detecting means theconcentration of removables in the fluid passing through the firstfilter, and can restart the recirculation when the concentration risesabove a second predetermined value.

If the first filter breaks down or the second filter crumbles, thefiltered water will contain removables that should have been filteredout, and this will create a problem during reuse. However, if a failureis detected, recirculation can be started immediately. This will preventproducing filtered water containing removables that should have beenfiltered.

The invention also can suck the fluid through the first filter.

For a sucking type, the reservoir tank of an open type can be used inwhich the fluid is stored and the filters are immersed. For apressurized type, the reservoir tank must be sealed, and hence, thisrequires a complicated construction.

An external force may be applied to the second filter surface. Becausethe second filter consists of removables that have aggregated, if anexternal force is applied, it is possible to remove the whole of thesecond filter or a surface layer of the second filter to refresh andmaintain the filtering performance.

The removables of the second filter surface can be desorbed with anexternal force. It is possible to desorb removables constituting a causeof clogging or forming gaps, and provide passages for fluids.

The first filter can be made of a polyolefin high polymer. The firstfilter can have resistance to alkalis and acids, and therefore, evenfluids with mixed chemicals can be filtered. Also, coagulatingsedimentation is possible with the first filter still immersed.

The removables can be inorganic solids or organic solids.

Each aspect of the method described below is separately illustrative ofthe various embodiments of the invention and is not intended to berestrictive of the broad invention.

A first aspect of the method is a method of fabricating a semiconductordevice , which comprises the steps of:

removing a processing waste in a fluid by passing through a filtercomprising at least a part of a processing waste generated in a step ofprocessing a semiconductor using the fluid.

A second aspect of the method is a method of fabricating a semiconductordevice according to the first aspect, wherein the step of processing asemiconductor comprises a step of mechanical processing a semiconductorusing the fluid.

A third aspect of the method is a method of fabricating a semiconductordevice according to the second aspect, wherein the step of mechanicalprocessing a semiconductor comprises a polishing step or grinding stepusing the fluid.

A fourth aspect of the method is a method of fabricating a semiconductordevice according to the first aspect, further comprising the steps of:

preparing a filter by passing the fluid including removables thorough afirst filter and depositing the removables on the first filter surfaceso as to form a second filter; and

filtering the removables by passing the fluid through the filter andthereby removing the removables from the fluid.

A fifth aspect of the method is a method of fabricating a semiconductordevice according to the fourth aspect, wherein the step of preparing afilter comprises the steps of:

passing the fluid including removables thorough the first filter anddepositing the removables on the first filter surface so as to form asecond filter while circulating.

A sixth aspect of the method is a method of fabricating a semiconductordevice according to the first aspect, wherein the step of processing asemiconductor comprises a step of dicing.

A seventh aspect of the method is a method of fabricating asemiconductor device according to the first aspect, wherein the step ofprocessing a semiconductor comprises a step of mirror polishing.

An eighth aspect of the method is a method of fabricating asemiconductor device according to the first aspect, wherein the step ofprocessing a semiconductor comprises a step of back grinding.

A ninth aspect of the method is a method of fabricating a semiconductordevice according to the first aspect, wherein the second filtercomprises processing waste of different sizes.

A tenth aspect of the method is a method of fabricating a semiconductordevice according to the first aspect, wherein the processing wastecomprise different sizes particles, and said second filter is made up ofpores which are larger than the smallest sizes of the particles andlarger than the largest sizes of the particles.

An eleventh aspect of the method is a method of fabricating asemiconductor device according to the first aspect, wherein said step ofremoving comprises a step of circulating the fluid for a constant timesince starting removing.

A twelfth aspect of the method is a method of fabricating asemiconductor device according to the eleventh aspect, wherein said stepof circulating comprises a step of detecting an inclusion degree ofprocessing waste included in the fluid passing through the filter, andstopping circulation of the fluid at the time point when the detecteddegree has fallen below a constant value.

A thirteenth aspect of the method is a method of fabricating asemiconductor device according to the twelfth aspect, wherein said stepof circulating comprises a step of detecting an inclusion degree ofremovables included in the fluid passing through the filter, andstarting circulation of the fluid again at the time point when thedetected degree has exceeded above a second constant value.

A fourteenth aspect of the method is a method of fabricating asemiconductor device according to the fourth aspect, wherein said stepof filtering comprises a step of filtering the fluid while suckingthrough the filter.

A fifteenth aspect of the method is a method of fabricating asemiconductor device according to the fourth aspect, further comprisinga step of applying an external force to a surface of the filter so thata constituent of the second filter can be moved.

A sixteenth aspect of the method is a method of fabricating asemiconductor device according to the fifteenth aspect, wherein saidstep of applying an external force comprises a step of applying theexternal force intermittently.

A seventeenth aspect of the method is a method of fabricating asemiconductor device according to the fifteenth aspect, wherein saidstep of applying an external force comprises a step of applying gas flowalong a surface of the first filter.

An eighteenth aspect of the method is a method of fabricating asemiconductor device according to the fifteenth aspect, wherein saidstep of applying an external force comprises a step of applying a forceso as to make a part of the constituent of the second filter released.

A nineteenth aspect of the method is a method of fabricating asemiconductor device according to the fifteenth aspect, wherein saidstep of applying an external force comprises a step of controlling aforce so that a thickness of the second filter is constant.

A twentieth aspect of the method is a method of fabricating asemiconductor device according to the fifteenth aspect, wherein saidfilter is disposed in perpendicular direction and said external forcecomprises a raising force of a bubble.

A twenty first aspect of the method is a method of fabricating asemiconductor device according to the fifteenth aspect, wherein saidstep of applying an external force comprises a step of applying amechanical vibration.

A twenty second aspect of the method is a method of fabricating asemiconductor device according to the fifteenth aspect, wherein saidstep of applying an external force comprises a step of generating asonic wave.

A twenty third aspect of the method is a method of fabricating asemiconductor device according to the fifteenth aspect, wherein saidstep of applying an external force comprises a step of generating a flowof the fluid.

A twenty fourth aspect of the method is a method of fabricating asemiconductor device according to the first aspect, wherein said firstfilter is made of polyolefin high polymer.

A twenty fifth aspect of the method is a method of fabricating asemiconductor device according to the first aspect, wherein said firstfilter has an uneven surface.

A twenty sixth aspect of the method is a method of fabricating asemiconductor device according to the fourth aspect, wherein said firstfilter has a bag typed filter in which clearance is formed and in whichsuction pipe for sucking is inserted.

A twenty seventh aspect of the method is a method of fabricating asemiconductor device according to the fourth aspect, wherein said secondfilter comprises Si.

A twenty eighth aspect of the method is a method of fabricating asemiconductor device according to the fourth aspect, wherein said secondfilter comprises mainly flake type of Si.

A twenty ninth aspect of the method is a method of fabricating asemiconductor device according to the first aspect, wherein saidprocessing waste comprises a processing agent used for mechanicalprocessing.

A thirtieth aspect of the method is a method of fabricating asemiconductor device according to the first aspect, wherein said fluidis reused after removing the processing waste.

Removables may comprise many kinds of form, such as flake typed Si.Hence, a good filter can be obtained without blocking.

If the removables are solids, small gaps of various shapes can be formedby the particles of differing diameter sizes. Consequently, smallerremovables can be trapped and also more passages for fluid can beprovided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a filter film of an embodiment of the invention.

FIG. 2 shows a filter film of an embodiment of the invention.

FIG. 3 shows a particle diameter distribution of silicon waste inwastewater produced during dicing.

FIG. 4 shows an exemplary filtering method of the invention.

FIG. 5 shows an exemplary filtering device used in the invention.

FIG. 6 shows an exemplary filtering device used in the invention.

FIG. 7 shows an exemplary filtering operation of FIG. 5 and FIG. 6.

FIG. 8 shows a system view illustrating an exemplary filtering method ofthe invention.

FIG. 9 shows a system in which an exemplary filtering method of theinvention is used for a dicing apparatus.

FIG. 10 shows a system view illustrating an exemplary filtering methodof the invention.

FIG. 11 shows an exemplary grinding or polishing method such asback-grinding.

FIG. 12 shows data for comparing an exemplary filtering system of theinvention with a conventional apparatus.

FIG. 13 shows a conventional filtering system.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention can remove removables (waste matter) from wastewater in astep of manufacturing a semiconductor device with a filter made ofremovables. The wastewater can contain mixed metal, inorganic or organicremovables. Removables are produced when slicing a crystal ingot intowafer form, when dicing, when back-grinding, when performing CMP(Chemical-Mechanical Polishing) or polishing a semiconductor wafer.

Examples of removables are Si, Si oxide, Al, SiGe, organics such assealing resin, and other insulating materials and metal materials. GaAsin compound semiconductors, would also be included.

Recently, dicing technique has been employed with CSP (Chip ScalePackage) manufacture. In dicing the surface of a wafer is coated with aresin and the sealed resin and wafer are diced together. Also,semiconductor chips are placed in the form of a matrix on a ceramicsubstrate, covered with a resin including the ceramic substrate, and thesealed resin and ceramic substrate are diced. Removables arise duringthose dicing processes.

Removables are also produced outside the semiconductor field. Forexample, in industries using glass such as liquid crystal panels, panelsof EL display devices and so on, glass waste as removables is producedwhen glass substrates are diced or substrate side faces are ground.Electric power companies and steel companies use coal as fuel. Fineparticles arising from coal constitute removables, and fine particlesmixed with smoke emerging from chimneys constitute removables. The samegoes for fine particles arising from the processing of ores, theprocessing of precious stones, and the processing of gravestones. Also,metal waste produced when working with a lathe or the like, and ceramicwaste produced during dicing and polishing ceramic substrates and thelike also constitute removables.

Removables arise when substances are polished, ground or milled, and afluid such as water or a chemical is supplied to remove the removables.Consequently removables are mixed into this fluid.

The invention will be explained with reference to FIG. 1 through FIG. 3.Removables can be various things, but the description below will assumethat an exemplary fluid is water and that removables from cutting,grinding, polishing, and milling processes are included in the water.

FIG. 1 shows a first filter film 10 and a filter pore 11. Films formedin layers on exposed parts of the filter pores 11 and the surface of thefirst filter film 10 are removables 12. The removables 12 are dividedinto large removables 12A and small removables 12B, which can passthrough the filter pores 11. Circled black dots represent the smallremovables 12B.

Filter films usable in principle are either organic high polymers suchas a polyolefin high polymer film or ceramics. Examples below usepolyolefin high polymers as filters.

Wastewater containing mixed removables is located above the first filterfilm 10 of FIG. 1, and filtered water filtered by the first filter film10 is located below the first filter film 10. Because wastewater is madeto flow in the direction of the arrows, and the wastewater is filteredusing the filter film 10, the water would descend naturally, but it canbe pressurized or made to move downward in the figure. The wastewater issucked from the side where the filtered water is. Although the firstfilter film 10 is disposed horizontally, it may alternatively bedisposed vertically as shown in FIG. 7.

As a result of the wastewater being pressurized or sucked through thefilter film as described above, the wastewater passes through the firstfilter film 10. The large removables 12A, which cannot pass through thefilter pores 11, remain on the surface of the first filter film 10.

A layer resulting from removables being trapped and remaining on thesurface of the first filter film 10 is utilized as a second filter film13.

Removables arising from machining work such as grinding, polishing ormilling are distributed in size (particle diameter) over a certainrange, and furthermore the shapes of individual removables aredifferent. Removables are suspended randomly in the wastewater in whichthe first filter film 10 is immersed. Large removables and smallremovables move toward the filter pores 11 in a random fashion.Initially, the removables 12B smaller than the filter pores 11 passthrough, but the removables 12A larger than the filter pores 11 aretrapped. The large removables 12A on the surface form a first layer of asecond filter film 13, and this layer forms filter pores smaller thanthe filter pores 11, and removables ranging from the large removables12A to the small removables 12B are trapped by these smaller filterpores. Because the shapes of the individual removables are different,gaps of various shapes form between the deposited removables, and watermoves through those gap passages and is filtered.

The second filter film 13 gradually grows as it randomly catches largeremovables 12A to small removables 12B, and starts to trap smallremovables 12B while providing passages for water (fluid). Furthermore,because the removables of the second filter film 13 just remain on thelayers and are easily movable, surface layers of the second filter film13 can be simply resuspended to the wastewater side by passing bubblesthrough the vicinities of the layers, applying a water flow, applyingsound or ultrasonic wave, applying a mechanical vibration, or rubbingwith a squeegee, for example. That is, even when the filtering capacityof the second filter film 13 drops, the capacity can be restored simplyby applying an external force to the second filter film 13The filteringcapacity is degraded mainly by clogging, and the removables responsiblefor clogging on the surface layer of the second filter film 13 can beeasily resuspended back into the fluid, and the clogging can beameliorated.

However, when the first filter film 10 is newly installed, because nolayer of removables 12 (second filter film 13) is formed on the surfaceof the first filter film 10, or when the second filter film 13 layer hasformed only a thin layer on the first filter film 10, the smallremovables 12B pass through the filter pores 11. The filtered water isrecirculated to the side where the wastewater is stored and monitored toconfirm that the small removables 12B are being trapped by the secondfilter film 13. Through such process, small-size removables like thesmall removables 12B passing through the filters are gradually trapped,and the wastewater is filtered to a predetermined cleanliness.

The above-mentioned confirmation can be faciliated if a detecting meanslike a light sensor 67 shown in FIG. 8 is provided so that theconcentration of the removables can be sensed.

When the second filter film 13 has not formed or when the smallremovables 12B remain in the filtered water, the filtered water isreturned to the wastewater side. During recirculation, the removables 12trapped by the filter pores 11 grow in layer to form a film, and thesecond filter film 13 on the surface of the first filter film 10provides various filter pore diameters and gradually traps removables ofsmall particle diameters to large particle diameters. The film graduallybecomes thicker and traps the small removables 12B having passed throughthe first filter film 10 and other removables of about the same size asand also smaller than the small removables 12B, and the filtered waterbecomes clean with almost no removables mixed it.

FIG. 2 shows a state where small removables 12B are trapped. After theconfirmation that removables of a desired size are not mixed in with thefiltered water (that they have become smaller than the predeterminedconcentration), the filtered water can be reused. Alternatively, thefiltered water may be returned to nature.

When the small removables 12B remain in the filtered water, thisfiltered water may not be returned, but may be moved to another tank.After it is confirmed that those small removables 12B and removables ofabout the same size as those small removables 12B are trapped, thefiltered water may be reused or returned to nature.

The wastewater stored above the second filter film 13 is graduallyconcentrated.

FIG. 3 shows a particle diameter distribution of waste arising duringdicing of a Si wafer. It is distributed over a range of about 0.1 μm to200 μm.

Because the particle diameter distribution measuring device could notdetect particles smaller than 0.1 μm, the distribution of waste smallerthan 0.1 μm is not shown. In practice, particles smaller than this existand are filtered effectively. In experiments, it was found that whenwastewater containing waste is filtered, the waste formed on the firstfilter film and trapped waste of below 0.1 μm.

For example if waste smaller than 0.1 μm are to be extracted, it isnormal to employ a filter formed with pores smaller than this size.However, even if filter pores of a size between a peak distribution oflarge particle diameters and a peak distribution of small particlediameters are used, waste of below 0.1 μm can still be trapped.

Conversely, if there was a single peak of particle diameter of theremovables at 0.1 μm, the filter would probably be clogged quickly. Ascan be seen from FIG. 3, two peaks—a large particle diameter and a smallparticle diameter—appear, and as a result of this the filtering capacityis increased. When observed with an electron microscope, it is foundthat the shapes of the cutting waste are diverse. Evidently, becausethere are at least two particle diameter peaks and the shapes of thecutting waste are diverse, various gaps form between waste particles toprovide passages for filtered water, and consequently there is littleclogging and a filter with a large filtering capacity is realized.

A filter of average pore diameter 0.25 μm was used as the first filterfilm 10. However if the distribution appears to shift to the right or tothe left to the one shown in FIG. 3, the pore diameter of the filter maybe changed according to that distribution. For example, if it appears toshift to the right, a pore diameter larger than 0.25 μm may be employed.Generally, if the pore diameter is increased, the number of removablespassing through the filter film increases, but if the time for whichfiltered water is returned to the wastewater is extended, almost all canbe trapped by the second filter film 13. Naturally, if the pore diameterof the filter is made smaller, the time needed to filter smallremovables becomes shorter.

FIG. 4 is an exemplary schematic of filtered water being returned to thewastewater side. FIG. 4 shows a raw water tank 20 or means (outer frame)for fixing the filters and a filter film 21.

The tank 20 (reservoir vessel)stores wastewater 22 above the filter film21, and stores filtered water 23 below the filter film 21. The filteredwater 23 is transported to various places by a pump 24 and directed by aswitching valve 25. Because there are removables passing through thefilter film 21, the valve 25 is switched so that filtered water isreturned to the tank 20. The filtered water is checked, and when theconcentration of removables reaches a desired value, or when removablesare virtually all removed, the valve 25 is switched and filtered wateris made to flow to the pipe 26. The resultant filtered water flowing tothe pipe 26 is a water free from removables or a filtered water of adesired concentration that can be reused. It can also be returned tonature as clean water. Filtered wastewater used for dicing can be usedfor dicing again. It can also be reused as water for washing solder orback-grinding, or cooling water.

In FIG. 4, suction was employed as a method for passing wastewaterthrough the filter but there are other methods such as gravity flowmethod and pressure method from the wastewater 22 side. Suction orpressurization technique can increase the filtering capacity.

The tank 20 is attached to pipes 27 and 28 and is sealed together.Filtration becomes possible if the pipe 27 side is pressurized orsuction is applied with the pump 24. In this example filter device isdisposed in a path through which water passes.

FIG. 5 through FIG. 8 illustrate a filtering device 35, which is placedor immersed in a raw water tank 50.

FIG. 5a shows a frame 30 shaped like a picture frame, and filter films31 and 32 fixed in place to face each other. Filtered water fills aninside space 33, enclosed by the frame 30 and the filter films 31 and32, and transported through a pipe 34 which sucks the filtered water in.Filtered water is taken out through the pipe 34 attached and sealed tothe frame 30. The filter films 31 and 32 and the frame 30 are completelysealed so that the wastewater does not enter the space 33 except throughthe filter films.

When the wastewater is sucked in, sometimes the filter film 31 of FIG.5a, a thin resin film, is distorted to the inner side and breaks.Consequently, to make this space as small as possible and make thefiltering capacity large, multiple inner spaces can be formed. This isshown in FIG. 5b. In FIG. 5b, only nine spaces 33 are shown, but manymore can be formed. The filter films 31 and 32 are made from apolyolefin high polymer film of thickness about 0.1 mm and in FIG. 5b,they are formed into a bag shape as FT. A frame 30 with a pipe 34 isinserted into this bag-shaped filter FT, and the frame 30 and the filterFT are in a face-to-face position. Two pressing means RG press the framefrom both sides to keep the FT fixed to the Frame. The FT is exposedthrough openings OP in the pressing means RG. The details will bedescribed with FIG. 6.

FIG. 5C shows a cylindrical filtering device 35. A frame attached to apipe 34 is cylindrical, and openings OP1 and OP2 are provided in theside face of the frame. Because the side face corresponding to theopenings OP1 and OP2 is removed, supporting means SUS for supporting thefilter film 31 are provided between the openings. A filter film isfitted to the side face.

The filtering device 35 will be described further in detail with FIG. 6.A part 30 a corresponding to the frame 30 of FIGS. 5(b) will bedescribed with FIG. 6b.

The part 30 a is in a shape that looks like a corrugated cardboard. Thinresin sheets SHT1 and SHT2 (0.2 mm each) are superposed; between themmultiple sections SC are provided in the vertical direction; and spaces33 are formed enclosed by the resin sheets SHT1 and SHT2 and thesections SC. The cross-section of the spaces 33 is a rectangle of length3 mm and width 4 mm. It is shaped as if many straws having thisrectangular cross-section have been lined up and integrated. The symbol30 a, because it keeps the filter films FT of both sides at a fixedspacing, is called a spacer.

In the surfaces of the thin resin sheets SHT1 and SHT2 of this spacer 30a, many holes HL of diameter 1 mm are opened, and the filter films FTare fitted to those surfaces. Filtered water filtered by the filterfilms FT passes through the holes HL and the spaces 33 and leavesthrough the pipe 34.

The filter films FT are fitted to the resin sheets SHT1 and SHT2 of thespacer 30 a. In the resin sheets SHT1 and SHT2 of the spacer 30 a thereare parts where holes HL are not formed. There is no filtering functionon the filter film FT corresponding to the parts where holes HL are notformed because wastewater does not pass through and parts whereremovables are not trapped arise. To prevent this phenomenon, aplurality of filter films FT are fitted. An outermost filter film FT1 isa filter film for catching removables, and toward the surface SHT1 ofthe spacer 30 a, a plurality of filter films having larger pores thanthe pores of the filter film FT1 are provided. In FIG. 6, an innerfilter film FT2 is provided next to the filter film FT1. Even at partsof the spacer 30 a where holes HL are not formed, because the filterfilm FT2 has large pores than those of the FT1, the entire face of thefilter film FT1 has a filtering function, and removables are trapped onthe entire face of the filter film FT1., The second filter film isformed by those removables over the entire front and rear faces of SHT1and SHT2. Although the filter sheets SHT1 and SHT2 are shown likerectangular sheets in FIG. 6b, they may be formed as bags as shown inFIG. 5b.

FIG. 6a, FIG. 6c, and FIG. 6d show how the baglike resin sheets SHT1 andSHT2, the spacer 30 a and the pressing means RG are installed.

FIG. 6a shows a perspective view of an exemplary filtering device 35,FIG. 6c shows a cut view from the head of the pipe 34 in the directionof the extension of the pipe 34 (the vertical direction), as shown bythe A—A line of FIG. 6a, and FIG. 6d shows a sectional view of thefiltering device 35 cut in the horizontal direction.

In FIG. 6c and FIG. 6d, the spacer 30 a is inserted into the bag-shapedfilter FT of FIG. 5b, and the four sides including the filter FT aresandwiched by the pressing means RG. The three sides closed in bag formand the remaining one side are fixed with an adhesive AD1 coated on thepressing means RG. Between the remaining one side (the open part of thebag) and the pressing means RG, a space SP is formed, and filtered waterproduced in the spaces 33 is sucked into a pipe 34 through the space SP.In the openings OP of the pressing means RG, an adhesive AD2 is providedall the way around, and they are completely sealed, so that fluid cannotenter except through the filter.

The spaces 33 and the pipe 34 are connected, and when the pipe 34 issucked, fluid passes through the pores in the filter films FT (FT1 andFT2) and the holes HL in the spacer 30 a toward the spaces 33, and thefiltered water can be transported from the spaces 33 via the pipe 34 tothe outside. The sheets SHT constituting the spacer 30 a, support thefilter films FT because areas other than where the holes HL are formedare made flat. Therefore, the filter films FT can maintain flat faces atall times, which help prevent breakage of the second filter film.

The operation of the filtering device 35 is shown schematically in FIG.7. If the pipe 34 is sucked with a pump in the direction as shown by thearrows without hatching, wastewater flows in through the filters and isfiltered.

A second filter film 36 is formed on the vertically disposed filtrationdevice by layers of removables trapped by the first filter films 31 and32. Because the second filter film 36 consists of solid removables whichhave aggregated, by applying an external force to the second filter film36, it is possible to remove the second filter film 36 entirely, orremove a surface layer of the second filter film 36. Removal can berealized simply by the ascending force of bubbles, a water flow, sound,ultrasound vibration, mechanical vibration, rubbing of the surface witha squeegee, or an agitator or their equivalents. And the immersedfiltering device 35 itself may be made to move in the wastewater (rawwater), and a water flow thereby produced on a surface layer of thesecond filter film 36 can remove the second filter film 36. For example,in FIG. 7, the filtering device 35 may be moved to the left and right asshown by the arrows Y about its base face as a support point. Becausethe filtering device itself moves, a flow can be created, and a surfacelayer of the second filter film 36 can be removed. If a bubblegenerating device 54 to be discussed in detail later is used for theabove-mentioned movable structure as well, bubbles can be made to strikethe entire filtration faces, and removed matter can be resuspended intothe wastewater efficiently.

If the cylindrical filtering device shown in FIG. 5C is employed, thefiltering device itself can be rotated about the centerline CL as anaxis, and the resistance of wastewater can be reduced. As a result ofthe rotation, a water flow arises on the filter film surface, andremovables of the second filter film surface layer can be transferredback into the wastewater, and the filtering capacity can be maintained.

In FIG. 7, as the method for removing the second filter film, an examplewherein the ascending of bubbles is utilized is shown. Bubbles ascend inthe direction of the arrows shown with hatching, and the ascending forceof those bubbles and bursting of bubbles apply an external forcedirectly to the removables. Also, water flow resulting from theascending force of bubbles and bursting of bubbles applies an externalforce to the removables. And as a result of this external force, thefiltering capacity of the second filter film 36 is constantly refreshed,and a substantially constant filtering capacity is maintained.

Another embodiment of the invention is related to the maintenance offiltering capacity. Even if clogging occurs in the second filter film 36and its filtering capacity falls, by applying an external force like thebubbles described above, removables constituting the second filter film36 can be transferred into the wastewater, thereby maintaining thefiltering capacity over a long period.

Depending on the way the external force is applied, there are twomethods of filtration. One is a method wherein the second filter film 36is completely removed. In this case, small removables pass through thefilter film because there are no removables layered on the first filterfilm. Until it is confirmed that small removables are being trapped, thefiltered water is recirculated to the water vessel (tank) containing thewastewater (raw water). Alternatively, though less efficient, filteredwater containing small removables can be moved to another water vesseluntil small removables are trapped on the film.

The second is a method wherein a film (removables which are the cause ofclogging) formed on the extreme surface of the second filter film 31 and32 is moved. Because removables causing clogging are mostly on theextreme surface of the filter film, by releasing them by an externalforce produced by means of, for example, bubbles, a constant filteringcapacity can be maintained at all times. This can be thought of askeeping the thickness of the second filter substantially constant byapplying an external force. It is a repitive cycle of removablesplugging the gaps and pores, external force agitating the extreme layerto unplug and open the gaps and pores, wastewater entering through theopened gaps and pores, and removables plugging the gaps and pores again.The filtering capacity can be maintained at all times by adjusting thesize of the bubbles, their amount, and the duration of the applicationof the bubbles.

To maintain the filtering capacity, the external force may be appliedconstantly or intermittently.

It is prefer that the filter film be completely immersed in the rawwastewater. If the second filter film is in contact with air for a longtime, the film may dry and flake or crumble. Even if it has just a smalllocation exposed to the atmosphere, the filter film will take in air andreduce the filtering capacity.

As long as the second filter film 36 can form on the first filter films31 and 32, the first filter films 31 and 32 may be made of sheet-formhigh polymer or ceramic and may be of the suction type or thepressurized type. However, the first filter films 31 and 32 arepreferably high polymer films and of the suction type.

The cost to make a sheet-form ceramic filter is high. If cracks form,leaks occur and filtering becomes impossible. For the pressurized type,the wastewater must be pressurized. For example, , the top of the tank50 in FIG. 8 must not be an open type but a closed type to applypressure. However, it is difficult to produce bubbles in a closed type.On the other hand, a high polymer film can be molded into various sheetsand bag-form filters. Since they are flexible, cracks do not form andforming concavities and convexities in sheets are easy. As a result offorming concavities and convexities, the second filter film lodges ontothe sheet, and flaking off into the wastewater can be suppressed.Furthermore if it is suction type, the tank can be an open type.

The pressurized type makes the formation of the second filter filmdifficult. In FIG. 7, if the pressure inside the spaces 33 is 1, apressure of more than 1 must be applied to the wastewater. Consequently,a load acts on the filter film, and also lodged removables are fixed byhigh pressure, and removables would probably not be dislodged easily.

A suction type mechanism in which a high polymer film is employed as afilter film is shown in FIG. 8.

FIG. 8 shows a raw water tank 50. Above the tank 50, a pipe 51 isprovided as a means to supply raw water. The pipe 51 passes fluidcontaining removables. For example, the pipe 50 may carry wastewater(raw water) containing removables out from a dicing apparatus, aback-grinding apparatus, a mirror polishing apparatus or a CMP apparatusused in manufacturing semiconductors. In the following example,wastewater will be assumed to contain silicon waste produced from adicing machine.

In raw water 52 stored in the tank 50, a plurality of filtering devices53 are immersed. Under these filtering devices 53, a bubble generatingdevice 54 is provided, and its position is adjusted so that bubbles passover the surface of the filter films. An air blower 55 is attached tothe bubble generating device 54.

A pipe 56 fixed to the filtering devices 53 corresponds to the pipe 34of FIG. 5 through FIG. 7. Filtered water filtered by the filteringdevices 53 passes through this pipe 56 and is selectively transportedthrough a first valve 58 to a pipe 59 on the tank 50 side and a pipe 60on a reuse (or draining) side A second valve 61, a third valve 62, afourth valve 63 and a fifth valve 64 are attached to the side wall orthe bottom of the tank 50. And attached to the end of a pipe 65 is aseparately provided filtering device 66.

The raw water 52 supplied through the second valve 61 is stored in thetank 50 and filtered by the filtering devices 53. Bubbles pass throughthe surfaces of filter films fitted to the filtering devices, andascending force and bursting of the bubbles move silicon waste trappedon the filter films. The bubbles are applied constantly to maintain thefiltering capacity.

When the filter films are newly fitted, or when it has been stopped fora long time because of a holiday, or when silicon waste is mixed in thepipe 56, the first valve 58 is used to recirculate the filtered waterthrough the pipe 59 to the tank 50. Otherwise, the first valve 58 isswitched to the pipe 60 and the filtered water is reused.

When the filter films are newly fitted, the recirculation time differsaccording to the size of the filter films, the amount of the siliconwaste, and the suction speed. However, second filter films can form onthe surfaces of the filter films in 4 to 5 hours. The formed secondfilter films are able to catch silicon waste of below 0.1 um in size.However, if the size of the filter films is small, approximately 30minutes is enough to form the second filter film. Accordingly, if therecirculation time is known, a timer may be set and the first valve 58may be automatically switched when a predetermined time has elapsed.

The frame (for example, a pressing means RG) of FIG. 6 in which thefilter films are mounted has the dimension of about 100 cm in height,about 50 cm in width, and about 5 to 10 mm in thickness. A plurality offiltering devices 35 with approximately 0.1 mm thick filter films areinstalled on both faces of the spacer 30 a.

When the removables are higher than a predetermined concentration, thefiltered water is determined to be irregular, and recirculation isautomatically started or a pump is stopped and filtering is stopped.During recirculation, since there is a risk of wastewater overflowingfrom the tank 50, fluid supply from the pipe 51 to the tank 50 may bestopped.

[1] In the case that filter films are newly installed to a frame(spacer).

Initially, when second filter films have not yet formed, the filteringcapacity is low. The wastewater is recirculated to form the secondfilter films with removables trapped on the filter films. The secondfilter films are grown to a state (below a first predetermined value)such that a target particle diameter is trapped by the second filterfilms, and after the formation of the second filter films, the firstvalve 58 is switched and filtered water is fed to the pipe 60 and thefiltration is started.

[2] In the case that filtering is stopped for holidays, long vacations,maintenance and the like and filtering is restarted.

Because the second filter films are made from removables and are inwastewater, when filtering is stopped for a long time, the filmscrumble. Recirculation restores the state of the second filter films.Filtered water is recirculated until the concentration of the removablesfalls below the first predetermined value, and thereafter the firstvalve 58 is switched and filtration is started. Bubbles are generated atleast when filtration is started.

[3] In the case that trapped removables are mixed back into wastewater.

When the second filter films partly crumble, or when the second filterfilms are disrupted, removables mix back into the filtered water.

When the second filter films have partly crumbled and the concentrationof the removables has become higher than a predetermined value (secondpredetermined value), recirculation is started to restore the secondfilter films. When the removables in the filtered water reaches apredetermined concentration (first predetermined value) the first valve58 is switched and filtered water is fed to the pipe 60 and filtrationis started. Bubbles are generated at least from the time filtration isstarted.

When the filter films are broken, it may become necessary to stop thepump 57 and replace the filter films or replace the filtering devices 53themselves. When the filter films are new, wastewater is recirculated asin [1]. Filtering devices whose filter films are not broken and havesecond filter films formed on their surfaces may be separately preparedand substituted. The second filter films may trap removables to thefirst predetermined value, and when they cannot, recirculation iscarried out. If they can, the first valve 58 is switched and filteredwater is fed to the pipe 60 and filtration is started.

[4] In the case that the level of the wastewater in the tank 50 fallsand the filter films contact the atmosphere. Before the filter filmscontact the atmosphere, the pump is stopped and filtering is stopped onthe basis of a level indicated by a sensor provided in the wastewater.Furthermore, bubbles may be stopped. Although wastewater is suppliedthrough the pipe 51 and the level of the wastewater rises, because thereis a risk of the second filter films crumbling under turbulence causedby the wastewater, the pump is stopped. And when the filtering devices53 is completely immersed in the waste water , the pump is started.During recirculation, removables are detected, and when the removablesin the filtered water have reached a predetermined concentration (firstpredetermined value), the first valve 58 is switched and filtered wateris fed to the pipe 60.

The first predetermined value and the second predetermined valueindicating the concentration of removables in the filtered water may bethe same, or the second predetermined value may deviate a certain amountfrom the first predetermined value.

A sensor 67 constantly senses silicon waste. The sensor 67 can be alight sensor with light-receiving/lightemitting devices. Thelight-emitting device may be a light-emitting diode or a laser. Thesensor 67 may be attached partway along the pipe 56 or partway along thepipe 59.

With time, the raw water becomes concentrated. And when it has reached apredetermined concentration, filtration is stopped, and using PAC, orAl₂(SO₄)₃ or the like, the raw water is made to undergo coagulatingsedimentation and left to stand. When this is done, the raw water in thetank generally divides into layers. Going from the upper layers to lowerlayers, the raw water is almost clear to completely opaque due toremovables. The raw water is collected by a selective use of the valves61 through 64.

For example, the almost clear raw water containing little silicon wasteis collected through the filtering device 66 by opening the second valve61. Then the valves 62 and 63 are successively opened and raw water iscollected. Concentrated slurry settling at the bottom of the raw watertank is collected by opening the valve 64.

If the fifth valve 64 is opened first, concentrated slurry flows underthe weight of the raw water, and water above the slurry also flows out,making the controlled collection of water difficult. For this reason,the valves are opened in the order 61, 62, 63, and 64 to collect the rawwater in a controlled manner.

In the lower middle of FIG. 8 (drawing surrounded by a dotted line) araw water level checking means 80 of the raw water tank 50 is shown. AnL-shaped pipe 81 is attached to the side face of the tank 50, anddepending on the raw water level at least one pipe 82 is attached. Theexternal diameter of the pipe 82 matches the internal diameter of thepipe 81 to fit onto the pipe 81.

As an example, when the level of the raw water reaches a positionslightly higher than the height at which the fourth valve 63 isattached, the pipe 82 can be fitted and a transparent viewing window canbe provided in the pipe 82 extending upward, whereby the level of theraw water can be checked. Accordingly, the raw water level can bechecked through the viewing window while raw water other than theconcentrated slurry is removed to the limit.

When the pipe itself is made of a transparent material such as glass,the raw water level can be checked without a separate viewing windowbeing provided. And this checking means may be pre-installed.

On the other hand, on the lower left of FIG. 8, a means for collectingthe water above the concentrated slurry to the limit is shown. That is,on the inside of the raw water tank 50, an L-shaped pipe 81 is mountedas shown in the figure. If an amount of silicon waste is specified, andif an amount of concentrated slurry is specified, the height of the headof the pipe 81 can be determined. Accordingly, if the head part of thepipe 81 or 82 is disposed in a place slightly higher than the top layerof the concentrated slurry, the raw water can be allowed to flow out ofthe filtering device 66 automatically to this height. Even if the fourthvalve 63 is opened accidentally, the outflow of raw water can be stoppedat the level of the head of the pipe 81 or 82. When the level of theconcentrated slurry changes, the pipe 82 can be removed to adjust thecollecting level of the raw water. Several pipes 82 may be prepared andany number of stages may be attached according to the level of rawwater.

Although a method for collecting concentrated water by coagulatingsedimentation has been described above, it may not be limited to this.For example, when the raw water 52 has reached a certain concentration,it may be moved to another filtering device 66 (FD). As an example, CMP(Chemical Mechanical Polishing) uses slurry with a chemical and abrasivegrains of below 0.1 μm. And during polishing, water is supplied, and aswastewater something whose concentration is slightly lower than theslurry is discharged. However as the concentration of the raw liquiddischarged increases as it is filtered, viscosity also increases. Sincethe polishing waste is very fine, the filtering capacity can rapidlyfall. Consequently, when a predetermined concentration is reached, thisraw liquid may be moved to another filtering device FD and filtered.That is, when filtering with the filtering devices 53 has continued andthe raw water has reached a predetermined concentration, it may be movedto another filtering device FD and filtered. For example, as shown inthe lower right of FIG. 8, the raw water may be fed to the upper side ofa filter FT1 and the raw water may be vacuum-sucked with a pump P. Andthis filtering device may be mounted in a concentrated recovery pipe forrecovery. The raw liquid is filtered through the filter FT1 and suckeduntil the highly concentrated raw liquid becomes somewhat solid.Meanwhile, as a result of the raw liquid being moved to the filteringdevice FD, the raw water level of the tank 50 falls; but dilute rawwater can be supplied through the pipe 51. When the raw waterconcentration thins and the raw water immerses the filters completely,filtration can start again.

The filtering devices FD and 66 can be used as removed particle recoverydevices. For example, when the raw water tank 50 containing siliconwaste of semiconductor wafers reaches a predetermined concentration,instead of performing coagulating sedimentation, the raw water may beseparated with the filtering device 66 (FD). Separated silicon waste isof high purity, and not having reacted with a chemical, it may bere-melted into ingots of Si for wafer use again. Furthermore, recoveredSi can be reused as materials for tiles, cement and concrete.

As described above, the system of FIG. 8 is made up of the raw watertank 50, the filtering devices (immersion/suction) 53, and the smallpump 57.

Because it is sucking at a low pressure (see FIG. 12) so that the firstfilters do not clog, the pump 57 can be a small pump. In the past,because only the raw liquid passed through a pump, the interior of thepump wore and the pump's life span was very short. However in thisconstruction, filtered water passes through the pump 57, and therefore,its life is greatly increased. Consequently, since the scale of thesystem can be made small, electricity costs for operating the pump 57can be reduced to about ⅕ to ¼ the cost of the prior operation and alsopump replacement costs can be greatly reduced, and with the initial costreduction of ⅓ and the running cost reduction overall of ⅕, it ispossible to greatly reduce maintenance costs. According to theexperimental results, 1 year operation without maintenance is possible.

And as shown in FIG. 5 through FIG. 7 the filtering devices 53 have asimple structure made up of the frame 30 for reinforcement and thefilter films 31 and 32 and the pipe 34 attached to the frame 30, andpipes for transporting filtered water.

The filter films are polyolefin films and their mechanical strength ishigh so they do not break even when dropped, and their resistance tochemicals such as acids and alkalis is high. Consequently, whereas inthe past, as shown in FIG. 12, the raw water concentration of about 300milligrams/liter was the maximum that was able to be handed. With thisapparatus, about three times the previous concentration, about 900milligrams/liter, can be handled, and direct chemical coagulatingsedimentation with the installed filter films can also be performed.

And when the raw water tank is used for coagulating sedimentation, extrapipes and pumps and so on become unnecessary, and a resource-savingfiltering system becomes possible. For example, with a system to whichfive dicing apparatuses are attached, performing coagulatingsedimentation once or twice are year is sufficient. Consider a 5-inchdicing wafer, which has a thickness of 625 μm, weighs 6 grams, and has ablade of 40 μm in width in the grooves of dicing depth 180 to 200 μm. Anaverage 160 of those are formed in a grid. One dicing wafer producesabout 0.3 grams (about 5% of one wafer) of sludge (silicon waste).

Because the filtering device performs its function by suction, as shownin FIG. 12, fine particles do not enter the fine pores of the filterfilms at low flow rate and low pressure. Furthermore, by forming thesecond filter films, the fine particles can be prevented from enteringinto the fine pores of the first filter films. Thus, the filteringperformance can be improved. By means of an external force such as airbubbles, continuous filtering is possible. The filtering (suction) ratecan be 0.3 to 0.5 meters/day, the filtering (suction) pressure can be0.2 to 0.1 Skg/cm², and the life of the filtering films can be expectedto be over five years. And the filtering speed and filtering pressureare set in a range such that there is no disruption of the second filterfilms because of breaking or deformation of the first filter films, andfiltering speeds of 0.01 to 5 meters/day and filtering pressures of 0.01kg/cm² to 1.03 Kgf/cm² (1 atmosphere) are essentially possible.

With the suction rate of 0.3 meters/day, 252 liters/(one filter film) ofraw water can be processed in one day, and with the suction rate of 0.5meters/day, 450 liters/(one filter film) of raw water can be processedin one day. The size of the frame of the filter can be about 100 cm×50cm×10 mm.

And in the dicing process, 3 to 5 liters/min of pure water may benecessary, and in a year 18000 tons may be used. To make pure water fordicing, it takes about 500 Yen to 1000 Yen/ton. However by using thissystem of the present invention, because filtered water can be reused,cost reduction is possible. As mentioned above, with the initial costbeing ⅓ the prior cost and since running costs overall can be reduced to⅕ the prior cost, the maintenance costs can be greatly reduced.

The concentrated raw liquid has been treated as industrial waste, andthe processing of this waste costs 3 million Yen/year. However byreusing filtered water, and reusing separated Si, the quantity of theconcentrated raw liquid can be essentially reduced to zero, and the rateof resource recycling can be about 97.6%.

Furthermore, the adhesion of silicon waste to the filter film interiorcan be prevented, and back-washing, which had hitherto been necessary,has become unnecessary.

Although the foregoing description was made with silicon waste arisingfrom a Si wafer as the removables, this invention can be utilized inother fields, as explained previously. In those fields, wastewatercaused damages to earth's environment, but by employing this inventionsuch damages can be greatly reduced For other examples of industrialwaste production, there are garbage incinerator plants that producesubstances having dioxins, uranium purifying factories that produceradioactive waste substances, and factories producing powders thatproduce harmful industrial waste substances. By employing the invention,waste having harmful substances can be removed regardless of the size ofthe harmful substances.

And if the removables are inorganic solids including at least oneelement among those of 2 a group through 7 a group, and 2 b groupthrough 7 b group in the periodic table, those removables can be almostcompletely removed by employing this invention.

The filtering system of FIG. 8 combined with a dicing apparatus systemis shown in FIG. 9. Some common parts in FIG. 8 are omitted in FIG. 9for brevity.

A semiconductor wafer W is attached to a table of the dicing apparatus.SW1 and SW2 are showers for spraying pure water on a dicing blade DB.SW3 is a shower for showering the wafer W and removes silicon wastearising from the wafer W during dicing. The shower SW3 may supply waterfrom above the wafer or from the side. The position of the shower SW3 isnot limited to a particular position. It is only necessary that a flowof water is produced on the wafer surface.

There is a receptacle BL below the wafer W for receiving wastewater, andthe pipe 51 connected to the raw water tank 50 is attached to a lowerpart of the receptacle tray BL.

Accordingly, as described above with reference to FIG. 8, wastewaterproduced in the dicing apparatus passes through the raw water tank 50and the filtering devices 53 and becomes clean water (filtered water)again, and is transported out through the pipe 56 and the pipe 60. Thefiltered water may be reused as pure water for the dicing apparatusthrough a pipe 71, or may be reused in another place through a pipe 72.If it is reused in another place, the pipe 71 is removed, and separatepure water is supplied through a pipe 70. The filtered water can also bereturned to nature.

An exemplary system will be explained using FIGS. 9 and 10.

Industrial-use water is stored in an industrial-use water tank 101. Theindustrial-use water is transported by a pump P1 through filters 102 and103 to a filtered water tank 104. The filter 102 is a carbon filter, andremoves debris and organic matter. The filter 103 removes carbon arisingfrom the filter 102.

The filtered water is transported by a pump P2 through a reverse osmosisfiltration device 105 to a pure water tank 106. This reverse osmosisfiltration device 105 uses reverse osmosis films, and waste (debris)below 0.1 μm is removed. The pure water of the pure water tank 106 istransported to a pure water tank 111 through a UV disinfection device107, adsorbing devices 108 and 109 and a device 110 for lowering theresistance of the pure water.

The UV disinfection device 107 as the name suggests disinfects the purewater with ultraviolet rays, and devices 108 and 109 are for removingions by ion exchange. A device 110 is for mixing carbon dioxide gas intothe pure water. When the resistance of the pure water is high, problemssuch as charging up of the blade arise. To prevent this the device 110deliberately lowers the resistance of the pure water.

Using a pump P3 the pure water is supplied to a dicing apparatus DM. At112, waste (debris) over the size of about 0.22 μm is removed again.

Then wastewater produced in the dicing apparatus DM is stored in a rawwater tank 113 using a pump P4, and filtered by a filtering device 114.The process is the same as that discussed in FIG. 5 through FIG. 8.Filtered water filtered by the filtering device 114 is returned to thefiltered water tank 104 and reused. Depending on the filter diameter andfiltering capacity of the filtering device 114, the filtered water maybe returned to the pure water tank 106, as shown by a solid line.

In the filtering device 114, when silicon waste is mixed with thefiltered water, it is returned to the raw water tank 113, as in FIG. 4.

The raw water tank 113 is the raw water tank 50 employed in FIG. 8, andby providing an immersed filtering device in the raw water tank 113, theraw water tank itself becomes a concentrated water tank, and the filterfilm also including silicon waste functions as a filter, and whensilicon waste is mixed with the filtered water, it is returned to theraw water tank using a valve similar to the valve 58 in FIG. 8.

A back-grinding apparatus is shown in FIG. 11. Even if this apparatus isinstalled in place of the dicing apparatus, because Si waste is stillmixed in with the wastewater the foregoing embodiment can be employed.

Like dicing back-grinding also has a turntable 200, and at least onewafer 201 is placed on this. From above a grindstone 202 is brought intocontact with the wafer, and the wafer rear face is ground. A nozzle 204is constructed so that filtered water can be supplied from a pipesimilar to the pipe 60 in FIG. 9 and FIG. 10 and reused. The turntable200 is a spool type and rotates, and the grindstone also rotates. Awastewater receptacle 203 receives wastewater produced in this grinding,and it is transported through the pipe 51 to the raw water tank 50.

When a filter is made with removables, filter pores smaller than theremovables constituting the filter can be formed, and through thosesmall pores still smaller removables can be removed. Consequently, it ispossible to remove sub-micron removables smaller than 0.1 μm.

When a fluid including removables is passed through the first filter anda second filter made of the removables is formed on the surface of thefirst filter, a second filter made up of pores smaller than the pores ofthe first filter can be made on the surface of the first filter, and itis possible to form a filter having a good filtering performance thatcan remove smaller removables.

Furthermore because it is made by removables being combined and gaps ofvarious shapes are formed between the removables, entry passages for thefluid can be provided.

As a result of the fluid including removables being recirculated throughthe first filter, a second filter made up of pores smaller than thepores of the first filter grows on the first filter surface, and becausesmall removables having passed through the pores of the first filteralso recirculate, it is possible to form a second filter that can trapsmall removables having passed through the pores of the first filter.

As a result of removables of different sizes being layered on the filterand the second filter, pores which the fluid can pass through and whichcan trap small removables can be formed.

As a result of the removables having a particle diameter distributionhaving two peaks and the size of the pores of the first filter beingbetween the two peaks, large removables of the particle diameterdistribution can be trapped. As the trapped removables are layered invarious forms, a second filter with small pores is formed, and becausegaps through which the fluid can flow are provided between the trappedremovables, it is possible to form a filter which can catch smallremovables and through which the fluid can pass.

Initially, filtered fluid in which small removables are mixed isproduced, but by recirculating, a filter can be made to trap even thosesmall removables. Accordingly, if determined that the removables havereached a predetermined degree of concentration, recirculation is thenstopped and filtration is started. It is possible to filter to a targetfiltering accuracy.

If there is a failure such as the first filter breaking down or thesecond filter crumbling, filtered water containing removables thatnormally should be trapped is generated, and has an adverse effect onthe reusability of the filtered water. However, when a failure isdetected, recirculation can be started immediately. Removables thatshould be trapped can be returned to the raw water tank and theproduction of filtered water containing the removables can be completelyprevented.

When it is a suction type, the storage vessel in which the fluid isstored and the filter is immersed can be an open type. When it is apressurized type, the storage vessel is a closed type and necessitates acomplicated structure.

Because the second filter is made by removables simply aggregating, ifan external force is applied, the whole of the second filter or asurface layer of the second filter can be removed, and it is possible torefresh the filtering performance and maintain the filteringperformance.

By using an external force, it is possible to remove removablesconstituting a cause of clogging and to form gaps between removables,and to provide passages for fluid.

Because a first filter made of a polyolefin high polymer has resistanceto alkalis and acids, filtering of fluids with chemicals also becomespossible. Also, coagulating sedimentation can be carried out with thefirst filter immersed.

As a result of the removables being solids and their particle diametersof being differing sizes, gaps of various shapes can be formed.Consequently, smaller removables can be trapped and more passages forfluid can be provided.

What is claimed is:
 1. A method of fabricating a semiconductor devicecomprising a step of: removing a processing waste in a fluid by passingsaid fluid through a filter, said filter comprising at least a part of aprocessing waste generated in a step of processing a semiconductor usingthe fluid.
 2. A method of fabricating a semiconductor device accordingto claim 1, wherein the step of processing a semiconductor comprises astep of mechanically processing a semiconductor using the fluid.
 3. Amethod of fabricating a semiconductor device according to claim 2,wherein the step of mechanically processing a semiconductor comprisespolishing or grinding using the fluid.
 4. A method of fabricating asemiconductor device according to claim 1, further comprising the stepsof: preparing a filter by passing the fluid including removables througha first filter and depositing the removables on the first filter surfaceso as to form a second filter; and filtering the removables by passingthe fluid through the filter and thereby removing the removables fromthe fluid.
 5. A method of fabricating a semiconductor device accordingto claim 4, wherein the step of preparing a filter comprises the stepsof: passing the fluid including removables thorough the first filter anddepositing the removables on the first filter surface so as to form asecond filter while circulating.
 6. A method of fabricating asemiconductor device according to claim 4, wherein said step offiltering comprises a step of filtering the fluid while sucking throughthe filter.
 7. A method of fabricating a semiconductor device accordingto claim 4, further comprising a step of applying an external force to asurface of the filter so that a constituent of the second filter can bemoved.
 8. A method of fabricating a semiconductor device according toclaim 7, wherein said step of applying an external force comprises astep of applying the external force intermittently.
 9. A method offabricating a semiconductor device according to claim 7, wherein saidstep of applying an external force comprises a step of applying gas flowalong a surface of the first filter.
 10. A method of fabricating asemiconductor device according to claim 7, wherein said step of applyingan external force comprises a step of applying a force so as to make apart of the constituent of the second filter released.
 11. A method offabricating a semiconductor device according to claim 7, wherein saidstep of applying an external force comprises a step of controlling aforce so that a thickness of the second filter is constant.
 12. A methodof fabricating a semiconductor device according to claim 7, wherein saidfilter is disposed in perpendicular direction and said external forcecomprises a raising force of a bubble.
 13. A method of fabricating asemiconductor device according to claim 7, wherein said step of applyingan external force comprises a step of applying a mechanical vibration.14. A method of fabricating a semiconductor device according to claim 7,wherein said step of applying an external force comprises a step ofgenerating a sonic wave.
 15. A method of fabricating a semiconductordevice according to claim 7, wherein said step of applying an externalforce comprises a step of generating a flow of the fluid.
 16. A methodof fabricating a semiconductor device according to claim 4, wherein saidfirst filter has a bag typed filter in which clearance is formed and inwhich suction pipe for sucking is inserted.
 17. A method of fabricatinga semiconductor device according to claim 4, wherein said second filtercomprises Si.
 18. A method of fabricating a semiconductor deviceaccording to claim 4, wherein said second filter comprises mainly flaketype of Si.
 19. A method of fabricating a semiconductor device accordingto claim 1, wherein the step of processing a semiconductor comprises astep of dicing.
 20. A method of fabricating a semiconductor deviceaccording to claim 1, wherein the step of processing a semiconductorcomprises a step of mirror polishing.
 21. A method of fabricating asemiconductor device according to claim 1, wherein the step ofprocessing a semiconductor comprises a step of back grinding.
 22. Amethod of fabricating a semiconductor device according to claim 4,wherein the second filter comprises processing waste of different sizes.23. A method of fabricating a semiconductor device according to claim 1,wherein the processing waste comprises different size particles, andsaid filter is made up of pores which are larger than the smallest sizesof the particles and smaller than the largest sizes of the particles.24. A method of fabricating a semiconductor device according to claim 1,wherein said step of removing comprises a step of circulating the fluidfor a constant time since starting to remove the processing waste.
 25. Amethod of fabricating a semiconductor device according to claim 24,wherein said step of circulating comprises a step of detecting aninclusion degree of processing waste included in the fluid passingthrough the filter, and stopping circulation of the fluid at the timepoint when the detected degree has fallen below a constant value.
 26. Amethod of fabricating a semiconductor device according to claim 25,wherein said step of circulating comprises a step of detecting aninclusion degree of removables included in the fluid passing through thefilter, and starting circulation of the fluid again at the time pointwhen the detected degree has exceeded above a second constant value. 27.A method of fabricating a semiconductor device according to claim 1,wherein said first filter is made of polyolefin high polymer.
 28. Amethod of fabricating a semiconductor device according to claim 1,wherein said first filter has an uneven surface.
 29. A method offabricating a semiconductor device according to claim 1, wherein saidprocessing waste comprises a processing agent used for mechanicalprocessing.
 30. A method of fabricating a semiconductor device accordingto claim 1, wherein said fluid is reused after removing the processingwaste.
 31. A method of fabricating a semiconductor device according toclaim 1, wherein said processing waste comprises mixed metal, inorganicand organic removable materials.
 32. A method of fabricating asemiconductor device according to claim 1, wherein said processing wastecomprises at least one of Si, Si oxide, Al, SiGe, organic material, andglass.
 33. A method of fabricating a semiconductor device according toclaim 1, wherein said filter comprising at least a part of a processingwaste generated in a step of processing a semiconductor using the fluidwhen slicing a crystal ingot into a wafer form or when dicing,back-grinding, or polishing a semiconductor wafer.
 34. A method offabricating a semiconductor device according to claim 1, furthercomprising a step of separating the waste from the filter when a rawwater tank containing silicon waste of semiconductor wafers reaches apredetermined concentration.
 35. A method of fabricating a semiconductordevice according to claim 34, wherein said fluid is reused after theprocessing waste is removed therefrom.